The overarching objective of this work is to develop a novel, user-centric visual paradigm aimed at enhancing situational awareness by providing a clear, concise and effective visualization of large, complex and heterogeneous population health data. The project represents collaboration at the University of Utah between the Scientific Computing and Imaging Institute, the Department of Pediatrics, the Department of Medicine and the Department of Biomedical Informatics. To inform the design of our system, we conducted contextual interviews with experts in the domain of infectious disease epidemiology and population health. We created a database containing over 300,000 encounters 2007-2008 using data from Intermountain Healthcare and developed an ontology for the medical findings in this dataset. We successfully developed a novel software system, named Common Ground, which extends the concept of a disease weather map we developed in a prior project. The system enables users to visually explore and analyze a set of medical findings associated with encounters over a selected period of time. We released Common Ground as a free open source under the most permissive MIT license.